Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden.
Phys Chem Chem Phys. 2018 Dec 19;21(1):26-31. doi: 10.1039/c8cp05862h.
The isothermal compressibility and correlation length of supercooled water obtained from small-angle X-ray scattering (SAXS) were analyzed by fits based on an apparent power-law in the temperature range from 280 K down to the temperature of maximum compressibility at 229 K. Although the increase in thermodynamic response functions is not towards a critical point, it is still possible to obtain an apparent power law all the way to the maximum values with best-fit exponents of γ = 0.40 ± 0.01 for the isothermal compressibility and ν = 0.26 ± 0.03 for the correlation length. The ratio between these exponents is close to a value of ≈0.5, as expected for a critical point, indicating the proximity of a potential second critical point. Comparison of γ obtained from experiment with molecular dynamics simulations on the iAMOEBA water model shows that it would be located at pressures in the neighborhood of 1 kbar. The high value and sharpness of the compressibility maximum observed in the experiment are not reproduced by any of the existing classical water models, thus inviting further development of simulation models of water.
从 280 K 到 229 K 的最大压缩温度范围内，通过基于明显幂律的拟合，分析了从小角 X 射线散射（SAXS）获得的过冷水的等温和相关长度的压缩系数。尽管热力学响应函数的增加不是朝向临界点，但仍然有可能通过最佳拟合指数获得明显的幂律，等温和相关长度的最佳拟合指数分别为γ=0.40±0.01 和 ν=0.26±0.03。这些指数之间的比值接近一个约为 0.5 的值，如临界点所预期的那样，这表明潜在的第二个临界点接近。将实验中获得的γ与 iAMOEBA 水模型的分子动力学模拟进行比较，表明它将位于约 1 kbar 的压力附近。实验中观察到的高压缩系数最大值的尖锐程度，没有被任何现有的经典水模型所重现，因此需要进一步开发水的模拟模型。
